Ion implantation is a technique in semiconductor technology that is used for selectively implanting an impurity material into a semiconductor material. In ion implantation process, the impurity material is ionized in an ionization chamber. The ions are accelerated to form an ion beam with a preset energy. The ion beam bombards the surface of a wafer and enters the wafer to reach a depth associated with the energy.
An ion implanter usually transforms a gas-state or solid-state impurity material into a plasma in an arc chamber. The plasma is then guided out of the arc chamber to form an ion beam. The ion beam may undergo quality analysis to eliminate unwanted ion species and may be accelerated to have a preset energy and then be introduced to the surface of a wafer.
FIG. 1 depicts a cross-sectional view of an ion source of an existing ion implanter. The ion source includes: an arc chamber 100; a reflector 102, a filament 103, and a source gas inlet 104. The filament 103 is located on the sidewall of the arc chamber 100. When connected to a power supply, the filament 103 heats up to generate thermo-electrons. The reflector 102 is located on sidewall opposite to the filament 103. The reflector 102, when connected to a power supply, is used to reflect the thermo-electrons generated by the filament 103 in order to prevent the thermo-electrons from being lost through the body of the arc chamber 100. The source gas inlet 104 is located at the bottom of the arc chamber 100, for passing an ion source gas into the arc chamber 100. The ion source gas is ionized into a plasma by colliding with the thermo-electrons generated by the filament 103. The plasma is then guided out of the arc chamber 100 through an outlet slit 101 at the top of the arc chamber 100.
When the ion source generates the plasma, associated by-products or impurity particles are formed in the arc chamber 100 and adhered to the inner surface of the arc chamber 100. A layer of conductive film is formed on the inner surface of the arc chamber 100. The layer of conductive film may also be formed on the filament 103 and the reflector 102. The conductive film tends to cause short-circuit of the filament 103. In addition, the conductive film can be easily fallen off from the inner surface of the arc chamber 100. When the conductive film falls on or near the filament 103, the stability of the filament 103 is affected. The service life of the implanter is significantly reduced.